This invention relates to optical communications systems, and in particular to a device for diverting light among various optical transmission elements.
In optical communications systems, the need exists for a variety of coupling devices where light can be switched among various transmission elements. For example, 1.times.2 and nonblocking 2.times.2 switches will be used in a variety of applications. In ring networks, for example, an asymmetric four-port coupler could be utilized. (See, for example, U.S. patent application of F. H. Levinson, Ser. No. 396,118, filed July 7, 1982 and assigned to the present assignee now U.S. Pat. No. 4,486,071, which is incorporated by reference herein.) It would be desirable if such couplers had a sparing feature so that a particular terminal in the network could be easily decoupled therefrom in the event of a malfunction in that station. Another type of coupler could find use in optical systems where a multiplexed signal is transmitted among many subscribers (e.g., Cable TV). Such a coupler would perform the function of a tunable demultiplexer to permit the subscriber to choose among the various transmitted wavelengths. In general, regardless of the particular function, it is desirable for the coupler to be as compact and as inexpensive as possible.
At least one proposal has been made for a multiport coupler using a graded-index-of-refraction lens. (See U.S. Pat. No. 4,304,460 issued to Tanaka et al.) There, an array of fibers is coupled to one surface of the lens and a rotatably mounted mirror positioned at an angle to the lens is provided at the other surface. Incoming light from one fiber is diverted to another selected fiber by a proper rotation of the mirror. A filter element can be provided between the lens and mirror and also rotated to perform multiplexing. Further, it is suggested that the angle of the mirror to the lens surface can be varied by piezoelectric driving means. While adequate, the need for a motor to rotate the element adds complexity and cost to the coupler and use of piezoelectric driving means is not considered to be optimum for alignment and low cost manufacture.
It has also been proposed to form a multiplexer/demultiplexer utilizing a graded-index-of-refraction lens and a diffraction grating at the surface of the lens opposite to the transmission elements. (See U.S. Pat. No. 4,111,524 issued to Tomlinson.) However, such a device does not provide a tunable feature.
It is an object of the invention to provide compact optical coupling devices which can divert light among various transmission elements in a controlled manner.